Exopeptidase

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An exopeptidase is an enzyme that catalyses the removal of an amino acid from the end of a polypeptide chain. Used for N-terminus or C-terminus determination of a protein. Exopeptidase cleaves the end of a polypeptide chain.

Exopeptidase Digestion

AMPM, CPAB, CPPA

AMPM: Aminopeptidase M digestion Aminoacids are released successively from the N-terminal of the peptide.

Acetylated N-terminals block release completely. Proline (Pro) is released only very slowly (see topics CPAB and TAB2).

CPAB: Digestion with a mixture of carboxypeptidases A+B Carboxypeptidases release aminoacids in succession from the C-terminal of a peptide. If the digestion is interrupted before it is complete, those aminoacids nearest to the C-terminal of the peptide will be present in higher analytical concentrations. When an aminoacid is released only slowly by an exopeptidase, the faster released aminoacids which follow it will be present in similar concentrations.

Arginine and proline (Arg and Pro) are not released by carboxypeptidase A, aspartic acid, cysteine, glutamic acid, glycine and lysine (Asp, Cys, Glu, Gly and Lys) are released only slowly.

Carboxypeptidase B releases arginine and lysine (Arg and Lys) rapidly (see topic TAB2). Proline (Pro) provides a complete block to carbopeptidases, neither it, nor its C-terminal neighbour being released.

Refer to topic EXOP for mass to use, and topic TAB2 for time to use.

CPPA: Carboxypeptidase A digestion Gives longer digestion time than CPAB for Lys, and no digestion for Arg. Seldom used on its own. (See topics CPAB and TAB2)

Refer to topic EXOP for mass to use, and topic TAB2 for time to use.